Icebergs, blue carbon and Antarctic climate feedbacks

DAVID DKA BARNES; ANDREW FLEMING ; CHESTER J. SANDS; MARIA LILIANA QUARTINO; DOLORES DEREGIBUS

PHILOSOPHICAL TRANSACTIONS OF THE ROYAL SOCIETY B-BIOLOGICAL SCIENCES

ROYAL SOC

Año: 2018

0962-8436

Sea ice, including icebergs, have a complex relationship with the carbon held within animals (blue carbon) in the polar regions. Sea ice losses around West Antarctica?s continental shelf generate longer phytoplankton blooms but also make it a hotspot for coastal iceberg disturbance. This matters because in polar regions ice scour is one of the few limitations on blue carbon ecosystem services, which work as a powerful negative feedback on climate change (less sea ice ? longer phytoplankton blooms ? more benthic growth ? more seabed carbon sequestration). As well as resetting succession of biota on the seabed (thus maintaining regional biodiversity) icebergs also fertilize the ocean with nutrients, generating phytoplankton blooms, which in turn cascade carbon capture into seabed storage and burial by benthos. Small icebergs scour the coastal shallows, whereas giant icebergs ground offshore in the deeper continental shelf. Most icebergs are small and their activity, especially seabed scouring, is difficult to monitor remotely and expensive in time/effort to record from research stations. However giant icebergs are easily tracked by satellite observation. Analysis of iceberg path and interaction with seabed showed that, in contrast to small coastal iceberg scouring, West Antarctica is a coldspot for giant iceberg interactions. Most giant icebergs and their scour hotspots are in East Antarctica. Giant icebergs create new blooms in the large ?gaps? they leave where they were attached to ice shelves, but whilst travelling they also enrich surface waters with nutrients greatly enhancing phytoplankton blooms. Significant benthic communities establish where iceshelves distintegrate (i.e. underneath where giant icebergs calved), and such benthos can rapidly grow to accumulate massive blue carbon storage. These are important because they are on deep continental shelves ? shallow enough to be in contact with phytoplankton bloom (sustained food) but deep enough to be beyond most iceberg scour, so with strong sequestration potential. When 5000 km2 giant icebergs calve off the Larsen C and Brunt iceshelves, we estimate they generate ~106 tonnes of immobilized zoobenthic carbon year-1. However giant icebergs (e.g. A23 and B15) collide with the continental shelf crushing and recycling vast benthic communities, which otherwise act as long-term stores of seabed carbon. In addition the reduction in buttressing of adjacent ice sheet typically increases flow seawards, albedo (more blue open water) and thus heat absorption, which increase sea-level. The costs of grounding scour are here estimated at 4 x104 tonnes carbon per year. We calculate that giant iceberg formation (ice shelf disintegration) has net potential of ~106 blue carbon sequestration benefits as well as more widely known negative impacts.